1. Field of the Invention
The present invention relates to a bonded honeycomb segment assembly. More particularly, it relates to a bonded honeycomb segment assembly which is excellent in thermal shock resistance.
2. Description of the Related Art
As a collecting filter for an exhaust gas, for example, as a diesel particulate filter (hereinafter referred to also as “DPF”) for collecting and removing a particulate material (hereinafter referred to also as “PM”) included in an exhaust gas from a diesel engine or the like, a honeycomb structure is broadly used.
Such a honeycomb structure usually has a constitution in which a plurality of cells as fluid passages partitioned by porous partition walls made of silicon carbide (SiC) or the like are provided in parallel with one another in the fluid passage direction. Moreover, the ends of the adjacent cells are alternately plugged so as to form a checkered pattern. That is, one cell has one end opened and the other end plugged, and another cell adjacent to this cell has one end plugged and the other end plugged.
The cells are plugged in this manner, whereby the exhaust gas flows into a predetermined cell (an inflow cell) from one end thereof, passes through the porous partition wall, and is discharged through a cell (an outflow cell) adjacent to the inflow cell. When the exhaust gas passes through the partition walls, the PM in the exhaust gas is collected by the partition walls, whereby the exhaust gas is purified.
To use such a honeycomb structure continuously for a long period of time, the structure needs to be periodically subjected to a regeneration treatment. That is, to decrease a pressure loss which increases owing to the PM deposited in the filter with an elapse of time and to return the performance of the filter to an initial state, the PM deposited in the filter needs to be burnt and removed. There has been a problem that a large heat stress is generated during the regeneration of the filter, thereby causing defects such as cracking and breakdown in the honeycomb structure. As the honeycomb structure which meets a demand for the improvement of a thermal shock resistance against this heat stress, there is disclosed a honeycomb structure having a divided constitution in which the honeycomb structure is divided into a plurality of honeycomb segments, and the segments are bonded via bonding layers to form a bonded article, thereby imparting a function of scattering and alleviating the heat stress (e.g., see Patent Document 1).
However, in recent years, a demand for improvement of the regeneration margin of the filter has further risen. When the regeneration margin of the filter improves, the amount of the deposited PM before performing the regeneration treatment increases, and hence the heat stress generated during the regeneration also increases. In the disclosed honeycomb structure, the thermal shock resistance does not sufficiently improve. When the improvement of the thermal shock resistance is realized, the bonding layers for integrally bonding the plurality of honeycomb segments require an excellent stress alleviating function and a high bonding strength. As the honeycomb structure for a purpose of the improvement of the thermal shock resistance by such improvement of the bonding layers, another honeycomb structure is disclosed in which the Young's modulus of the material of the bonding layers for bonding the honeycomb segments is set to 20% or less of that of the material of the honeycomb segments (e.g., see Patent Document 2).
Still another honeycomb structure is disclosed in which the Young's modulus of the bonding layers made of a predetermined material is set to 3 GPa or more, thereby suppressing the deformation of bonding members due to a heat strain. Furthermore, the breakdown of the bonding layers due to the stress is suppressed to improve the thermal shock resistance (e.g., see Patent Document 3).
[Patent Document 1] U.S. Pat. No. 4,335,783
[Patent Document 2] JP-A-2001-190916
[Patent Document 3] JP-A-2008-179526